[6] Puget Sound Orcas Part Of Slow Food Movement
It hasn't been the most glamorous field work for NOAA researchers but someone had to do it--follow ESA-listed killer whales around the San Juans in a small boat scooping up bits of poop and vomit from southern resident orcas to get better clues about their diet. And as they had suspected, local salmon, especially chinook, make up a good part of it.
"Our findings identified specific Chinook stocks from Canada's Fraser River that fish managers need to pay particular attention to because these killer whales are so dependent on them," said Dr. Brad Hanson, lead author of the study and a marine mammal scientist with NOAA's Northwest Fisheries Science Center in Seattle.
The study, titled "Species and stock identification of prey consumed by endangered 'Southern Resident' killer whales in their summer range" was published in the journal Endangered Species Research. Collaborators included scientists from the Department of Fisheries and Oceans Canada and in Washington, Cascadia Research Collective, the Center for Whale Research, the University of Washington and the Washington Department of Fish and Wildlife.
The scientists estimated that up to 90 percent of the chinook eaten by the whales were from BC's Fraser River. The whales ate mostly salmon from the Upper Fraser in June, the Middle Fraser in July, and from the South Thompson and Lower Fraser in August and September. Just a small fraction of the samples collected came from Puget Sound rivers.
One surprise finding was that the orcas don't seem much interested in pursuing sockeye--the Fraser's main product.
"The result from the present study will allow fish managers to potentially fine tune their activities to meet both salmon and whale recovery goals," said the authors. "For example, our results suggest that the whales may be particularly dependent upon Fraser River chinook salmon stocks during the summer months. In considering the risk of fisheries to the whales via prey reduction, it may therefore make sense to pay particular attention to fisheries that impact these stocks."
They also said their results may help assess the potential importance of hatchery chinook in meeting the whale's prey requirements.
But they pointed out that the orcas spend most of their time in outer coastal waters between fall and spring. ranging from central California to northern BC. "It will therefore be important to conduct similar studies in outer coastal areas in order to gain a more complete understanding of the whales' diet.
They said the next steps involve assessing the impact on Fraser chinook stocks from the three southern resident orca pods, "as well as providing more realistic estimates of the intake of persistent organic pollutants than those of a recent analysis (Cullen et al, 2009)."
The Cullen paper suggested the southern resident whale population may be ingesting four times as much PCBs [polychlorinated biphenyls] by body weight as the northern BC orca population (see NW Fishletter 257).
Since the disappearance of seven southern resident orcas in recent years, including two reproductive females, scientists have been taking a closer look at the whales' diet, hoping to find clues to their decline. Some whale advocates had been quick to blame reduced chinook runs for the problem, especially in Puget Sound and the Columbia River. They also pointed to high PCB levels in Puget Sound chinook as another harmful factor.
However, the Cullen paper showed that chinook from the lower Fraser River carried higher PCB levels than Duwamish River chinook from mid-Puget Sound, but lower levels than salmon from the Deschutes River at the southern end of the Sound.
NOAA researcher Hanson said others have also found lower PCB levels in salmon during the winter off California than a study cited in the Cullen paper. Columbia River and Sacramento River chinook contain about half the PCB levels of the Puget Sound chinook.
Latest addition to the orca pod with mother near Victoria, BC in February.
Photo by David Ellifrit, Center For Whale Research (taken under NOAA permit)
But local orca numbers have been increasing lately. Another birth last month has brought the southern population up to 89 members, the highest in five years. It's the seventh birth this year, a record number for the last 20 years or so. Usually, only about half of the calves survive their first year.
By 1973, the southern resident population had declined to 71. Then it climbed to 99 by1996, then dropped to 79 six years later.
It was reported that the southern residents have been spending a lot of time off the west coast of Vancouver island this winter, where Columbia river fall chinook are known to graze. This year's fall chinook run is expected to be very robust, and their improved numbers may be helping to boost whale numbers as well.
Hanson told NW Fishletter, that, at the moment, he has no idea where the resident orcas are. He said none had been sighted off California this past winter, but one had been seen off the Oregon coast at the end of February. (For more information on orca sightings, see orcanetwork.org.) -B. R.
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